Many state and local codes prohibit wood burning appliances in bedrooms and/or venting more than one thing into a single chimney. If the furnace, water heater or a first floor fireplace is vented into this chimney you definitely do not want an opening for CO to leak from in the place you sleep, code or no code.

If this is an unused chimney and there are no fireplace- in-the-bedroom restrictions you might be able to install a pre-fab unit, but weight would likely become an issue.